A polishing composition for use in formation of a wiring structure in a semiconductor device is required to have a high capability for polishing a conductive metal such as tungsten and have a low capability for polishing an insulator such as silicon dioxide. This is intended for inhibiting the occurrence of erosion on the surface of the semiconductor device.
For forming the wiring structure, a conductor layer 13 composed of a conductive metal is generally formed on an insulator layer 11 having trenches 12 on the surface (see FIG. 1). Thereafter, the conductor layer 13 is polished so that the insulator layer 11 in areas other than trenches 12 is exposed (see FIG. 3). Erosion refers to a phenomenon in which as shown in FIG. 4, the insulator layer 11 between neighboring trenches 12 in an area where trenches 12 are densely formed is excessively polished, whereby the surface of the insulator layer 11 in the area is recessed in the direction of thickness of the insulator layer 11 as compared to the surface of the insulator layer 11 in other areas. The degree of recess of the surface of the insulator layer 11 at this time is represented by erosion amount e (see FIG. 4). The erosion increases wiring resistance of the semiconductor device and reduces flatness thereof.
Japanese Laid-Open Patent Publication No. 10-265766 discloses a first conventional polishing composition containing hydrogen peroxide and iron nitrate. The first conventional polishing composition has a high capability for polishing tungsten owing to a synergistic effect of hydrogen peroxide and iron nitrate. However, iron ions originating from iron nitrate may remain in a semiconductor device polished with the first conventional polishing composition. The remaining iron ions cause surface defects to occur in the semiconductor device and degrade electrical characteristics of the semiconductor device.
On the other hand, Japanese National Phase Laid-Open Patent Publication No. 2000-501771 discloses a second conventional polishing composition containing ammonium persulfate and potassium periodate. The second conventional polishing composition has a high capability for polishing tungsten owing to a synergistic effect of ammonium persulfate and potassium periodate. However, it also has a high capability for polishing silicon dioxide. Therefore, the second conventional polishing composition does not inhibit erosion.